The Stock Exchange of Thailand is undertaking a major revision of its rules to boost market confidence, responding to concerns that numerous measures introduced over the past 2-3 years have become obstacles to investment and market liquidity.

A key highlight is narrowing the Tick Size for stocks priced between 2 and 50 baht, helping reduce price gaps, making trading easier and lowering costs. This includes efforts to maintain balance by imposing an Extra Charge fee on accounts submitting abnormally frequent orders.

However, some measures such as Minimum Resting Time and Dynamic Price Band have been canceled, reflecting a new perspective aimed at reducing system burdens and enabling price mechanisms to operate faster and more efficiently, thereby restoring liquidity and confidence in the Thai stock market over the long term.

Reasons for the major rule revisions revealed.

The Stock Exchange of Thailand (SET). SET is moving forward with a comprehensive update of trading regulations to align with current market conditions, while inviting public feedback from all sectors. The focus is on reducing costs, increasing liquidity, and removing investment barriers.

Assadej Kongsiri, Director and Managing Director of the Stock Exchange of Thailand (SET). He disclosed that SET has consulted with member companies and issued a consultation document to gather further opinions before submitting the proposals to the Securities and Exchange Commission (SEC) for approval.

Over the past 2-3 years, SET has continuously listened to feedback from all sectors. It acknowledges that while many measures were implemented, opinions have varied—some positive, others viewing the number and scope as excessive.

Therefore, in this review, SET aims to establish a more stable context for investors than in the past, conducting detailed trading data analysis and discussions with securities companies, fund management firms, foreign institutional investors, retail investors, and experts from various fields.

The goal is to consider which measures need adjustment to best balance the interests of all parties under current market conditions.

. Rongrak Panapawutikul, Deputy Managing Director, Head of Legal and Corporate Risk Management, SET. He stated that SET has monitored and reviewed current measures and found the need for modifications, leading to this round of improvements focusing on flexibility to suit the current volatile market environment.

He emphasized the importance of raising market quality, promoting fairness, and building investor trust and confidence.

Summary of the public hearing on new measure adjustments.

The rule revisions can be categorized into three groups of measures.

The changes include adding 2 new measures, revising 3 existing ones, and canceling 3 measures, detailed as follows.

Group 1: Measures to enhance market quality, fairness, and efficiency (new measures).

1. Narrowing the Tick Size range. SET has narrowed the price increment intervals for securities priced between 2 and 50 baht, focusing especially on the 10-25 baht range, to align with international markets.

This reduction helps decrease price spreads, lowering trading costs for all investors and increasing the likelihood of order matching, thereby improving overall market liquidity.

2. Introducing an Extra Charge fee on accounts with high Order-to-Trade Ratio (OTR). This fee applies to accounts submitting a large volume of orders with relatively few trades executed, specifically those with an OTR exceeding 100 times and more than 50 orders per minute.

The charge applies only to orders exceeding 30,000 per day, at a rate of 0.15 baht per order, calculated daily. This reflects the true cost of order submission and reduces system burden.

This measure excludes and does not apply to Market Makers (MM) sending orders.

Group 2: Measures to reduce abnormal price volatility.

3. Revised Uptick Rule for short selling. The new rule returns to a Zero-Plus Tick price for short sales under normal conditions. The Uptick Rule will apply only when a security’s closing price drops 10% or more from the previous day’s close, enforced individually on the next trading day to slow selling pressure during volatile periods. Market Makers are exempted.

4. Adjusted short-selling eligibility. SET narrows the list of securities eligible for short selling to highly liquid stocks only, including SET100 stocks, ETFs, DRs, and underlying securities of Single Stock Futures, while removing ETF underlying securities and DW underlying securities from the short-selling list.

5. Cancellation of the Dynamic Price Band (DPB). SET has removed this measure to reduce trading obstacles, noting it was frequently triggered on low-liquidity stocks by small trading volumes, adversely affecting investors and not effectively controlling volatility.

Group 3: Measures governing inappropriate trading behavior.

6. Revised High-Frequency Trading (HFT) registration. The approach changes from requiring HFT registration before trading to a "post-audit" method based on actual trading behavior.

This considers factors such as having a dedicated order submission channel (Dedicated API), submitting more than 50 orders per minute per account, end-of-day holdings under 50%, active trading on more than 80% of trading days, and daily trading values exceeding 30 million baht.

7. Removal of restrictions on securities HFT can trade. Since short-selling eligibility is now limited to highly liquid stocks and HFTs are monitored based on actual trading behavior, these restrictions are no longer necessary.

8. Cancellation of Minimum Resting Time (MRT). The rule requiring orders to remain on the book for at least 250 milliseconds is removed due to minimal triggering and low efficiency.

Additionally, with the introduction of the Extra Charge fee and AI monitoring of abnormal behavior, MRT is considered an unnecessary system burden.

The Stock Exchange of Thailand is accepting public feedback from 13 to 29 May 2026, aiming to maintain these new measures stable for at least 18 months after implementation to avoid frequent changes.

However, SET remains ready to review and adjust measures if significant market-impacting events occur.

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