Recently, Thai investors have often encountered a confusing scenario: the SET Index rises, yet portfolios show little gain, or on some days, the index appears stable while most stocks on the board are in the red.
The key reason for this lies in a single stock—DELTA—whose large size means its movements alone can sometimes reshape the entire Thai stock market's appearance on certain days.
According to data from the Stock Exchange of Thailand, the total market capitalization of the Thai stock market is about 19.37 trillion baht, while DELTA's market value is approximately 4.07 trillion baht, or around 21% of the entire market.
This means DELTA's price movements influence the index more than many other stocks combined.
The SET Index is designed to reflect the overall prices of all stocks in the market using a market capitalization-weighted method. Therefore, stocks with higher market caps affect the index more than smaller stocks.
The problem arises when a single stock becomes disproportionately large; the index's reflection may not represent the experience of most investors.
For example, today (22 May 2026) at 14:46, the Thai stock market rose to 1,533.58 points, up 2.91 points or +0.19% from the previous day. DELTA, which increased, impacted the index by 4.90 points—more than the total index gain—after its price rose to 331.00 baht, up 5.00 baht (+1.53%).
This is why many securities analysts have recently begun using the concept of "SET ex. DELTA," excluding DELTA's impact when assessing the market to see if buying interest is spreading to other stocks.
. Dao Securities (Thailand) Public Company Limited stated that when excluding DELTA's price changes, the Thai stock market index would show only slight gains or losses, or hardly change at all. This signals that investors are waiting for new positive factors or for existing negative factors to subside.
Therefore, they recommend focusing on "short-term trading frames," emphasizing trading within ranges and avoiding holding positions across weeks in large proportions.
DELTA is not just a large stock but one whose value has grown faster than the market in recent years, driven by global trends in Data Centers, Power Management, AI Infrastructure, and a booming electronics industry, attracting significant capital inflows and rapid price increases at times.
How large is DELTA compared to other big-cap stocks in the Thai market? Recent data show DELTA's market capitalization soaring to about 4.07 trillion baht, far surpassing previous market pillars like ADVANC and PTT, which stand at around 1.06 trillion baht.
This means DELTA alone is now almost four times larger than the second-largest stock on the board.
At this scale, DELTA carries the greatest weight in calculating the SET Index. Small price moves of a few baht in DELTA can significantly sway the entire market index sharply up or down.
Thus, many times when the market index shows strong gains or losses, it may not reflect the whole board but merely mirror buying or selling activity in DELTA alone.
On the other hand, DELTA's massive size means institutional investors who track benchmarks or index funds must trade accordingly. Therefore, when DELTA moves, money tends to flow into or out of DELTA, causing the index to appear stronger or weaker than most stocks actually are.
However, the outsized influence of a single stock is not new. The Stock Exchange of Thailand addressed this in 2025 by introducing capped weight rules limiting individual stock weights in the SET50 and SET100 indices to 10%, reducing overreliance on large stocks and making indices better reflect the overall market balance.
From early 2026 to now, DELTA's share price has surged sharply, rising over 88.44%, in line with the overall SET Index gain of 21.67%, attracting investor attention on the stock's future direction.
Amid expectations of soaring profits and a stretched valuation, leading securities analysts have recently assessed the situation as follows.
Kasikorn Securities Public Company Limited holds a positive view on performance, noting normalized profit in Q1 2026 reached 8.8 billion baht, up 77.0% year-on-year, exceeding the research team's forecast by 11% and the market's by 14%.
The main driver was better-than-expected gross margins. Management also anticipates continued growth in Data Center and AI segments, key businesses in 2026–2027, fueled by large company investments, projecting strong orders in the next 3-6 months.
However, their investment strategy recommendation is simply "hold" with a target price of 320.00 baht. Despite raising the target P/E to 92 times to reflect strong growth prospects, DELTA currently trades at a high P/E of 101 times and a PBV of 30 times for 2026.
They therefore advise investors to "wait to buy on price dips," as the current price is close to their target.
Meanwhile, Yuanta Securities (Thailand) Company Limited has upgraded its recommendation to "speculative buy," raising the target price to 283.00 baht per share from 208.00 baht, following DELTA's better-than-expected Q1 2026 normalized profit driven by strong gross margin growth.
They see profit trends remaining strong for the rest of the year, supported by AI demand and expanding gross margins from innovative new products, with signs emerging since late Q1.
However, they also caution about the stock's high valuation, noting that under the new estimates, the stock trades at a 2026 P/E of 96 times, which is considered stretched historically.
If profits do not meet expectations, the stock risks a valuation downgrade. Thus, they recommend a strategy to "accumulate on weakness" rather than chase prices after better-than-expected earnings.
Read stock and investment news with Thairath Money at
Follow the Facebook page: Thairath Money at this link