本研究旨在探討台灣股市初次上市櫃 (IPO) 公司在掛牌初期的期初報酬與股價波動率，並檢驗資訊不對稱理論在台灣市場的適用性。以臺灣上市櫃 IPO 案件為對象，區分電子業與非電子業子樣本，運用多元迴歸模型與穩健標準誤，分析公司特徵及承銷特徵對掛牌首日與首五日表現的影響。

期初報酬的實證結果顯示，台灣 IPO 蜜月行情深受大盤氛圍主導，資訊不對稱變數缺乏獨立解釋力。在納入市場報酬的模型中，大盤走勢與市帳值比呈現顯著影響；然而一旦剔除市場報酬，整體模型隨即失去顯著性，傳統資訊不對稱變數皆無法有效預測期初報酬。此外，隨著時間推移至掛牌第五日，微觀基本面的影響力快速收斂，報酬表現全面回歸系統性大盤走勢。

股價波動率的實證結果則顯示，資訊不對稱對風險的影響具有顯著的產業異質性，且保鮮期極其短暫。在首日波動率模型中，負債比顯著推升非電子業的波動，而公司規模則顯著降低電子業的波動，反映出不同產業在評價基礎與風險容忍度上的差異。在首五日波動率模型中，所有基本面與資訊不對稱變數皆全面失效。綜合而言，本研究指出資訊不對稱理論於台灣 IPO 市場之適用性，並非體現於傳統的期初報酬預測，而是深刻反映在短期波動率的風險衡量與產業異質性的價格發現機制上，為新股定價與市場風險控管提供了嶄新的視角。

This study investigates the initial returns and stock price volatility of Initial Public Offerings (IPOs) in Taiwan to examine the applicability of information asymmetry theory. Using multiple regression models with robust standard errors, this research analyzes the impacts of firm characteristics and underwriting characteristics, during the first and fifth days of listing across electronic and non-electronic industries. Empirical results show Taiwan's IPO initial returns are highly driven by market sentiment. When market returns are excluded, traditional information asymmetry variables lose explanatory power. For stock volatility, the impact of information asymmetry exhibits significant industry heterogeneity. Excluding market factors, the leverage ratio significantly increases first-day volatility in non-electronic firms, while firm size reduces it in electronic firms. However, these fundamental influences converge rapidly and completely disappear by the fifth trading day. In conclusion, this study contributes by demonstrating that the applicability of Information Asymmetry Theory in Taiwan's IPO market lies not in predicting absolute initial returns, but rather in explaining short-term volatility and the price discovery mechanisms driven by industry heterogeneity. This provides a novel perspective on IPO pricing and risk evaluation.

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