我國政府於2018 年進行一系列有關所得稅制優化之政策改革，包含將營利事業所得稅率由17%調升至 20%，以及廢除兩稅合一制度。隨後又於2019年陸續推出「智慧機械及5G投資抵減」與「未分配盈餘實質投資抵減」等租稅優惠政策，旨在透過租稅優惠引導企業進一步投資與轉型。本研究旨在探討此政策組合下，有效稅率與企業研究發展費用率之關聯性，並分析稅改前後企業研發投入行為之變動 。
本研究以2014年至2023年我國上市櫃公司（不含金融保險業）為樣本，區分稅改前（2014-2017）與稅改後（2020-2023）兩個期間進行實證分析。實證結果顯示：1.稅改後的研發費用率顯著高於稅改前，顯示租稅優惠政策帶來的正面激勵效果大於調升名目稅率之負面影響。2.落後一期之有效稅率與研發費用率呈顯著負相關，證實當企業面臨較高稅負壓力時，將會排擠其研發支出之預算配置。3.按企業規模大小分組下，大企業之研發投入對落後一期有效稅率變動較為敏感，小企業則較不受影響。4.按資產密集度高低分組下，高資產密集度公司較不受落後一期有效稅率變動影響，但在稅改後研發費用率顯著上升；低資產密集度公司於稅改後研發費用率並未顯著影響，但研究發展費用率與落後一期有效稅率呈顯著負相關。

In 2018, the Taiwanese government implemented a series of tax reforms aimed at optimizing the income tax system, which included raising the profit-seeking enterprise income tax rate from 17% to 20% and abolishing the integrated income tax system. Subsequently, in 2019, tax incentives such as "Investment Tax Credit for Smart Machinery and 5G" and " Deduction of Undistributed Earnings and Application for Tax Refund for Substantial Investment " were introduced to guide corporate investment and transformation. This study explores the relationship between the effective tax rate (ETR) and corporate R&D expenditure rates under this policy combination, analyzing changes in R&D investment behavior before and after the tax reform.
Using a sample of listed and OTC companies in Taiwan (excluding the financial and insurance industries) from 2014 to 2023, this study conducts an empirical analysis by dividing the timeframe into pre-reform (2014–2017) and post-reform (2020–2023) periods. The empirical results indicate: (1) R&D expenditure rates were significantly higher after the reform than before, suggesting that the positive incentives from tax credits outweighed the negative impact of the increased nominal tax rate. (2) There is a significant negative correlation between the lagged effective tax rate and the R&D expenditure rate, confirming that higher tax burdens create a crowding-out effect on corporate R&D budget allocation. (3) Grouped by firm size, R&D investment in large enterprises is more sensitive to changes in the lagged ETR, while small enterprises are less affected. (4) Grouped by asset intensity, high-asset-intensity companies are less affected by changes in the lagged ETR but showed a significant increase in R&D rates post-reform; conversely, low-asset-intensity companies showed no significant change in R&D rates post-reform, but their R&D expenditure maintained a significant negative correlation with the lagged ETR.

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