Sweet pepper is a tropical plant that thrives in warm climates. High temperature during hot summer months in Upper Egypt, however, highly reduces the yield and quality. The purpose of this experiment was to evaluate the performance and stability of nine pepper genotypes collected from Qena, Luxor and Aswan governorates planted in three planting dates (February, March, and May). Our findings showed that heat stress had a negative effect on most of the plant studied traits. Heat stress affected the vegetative, physiological and yield traits. All studied traits decreased by increasing the prevailing temperature except chlorophyll content, number of days to 50 % flowering, and No. of branches per plant. Heat stress decreased plant height, fresh weight, dry weight, and total leaf area and leaf area index. High negative correlations were observed between the prevailing temperature and plant fresh weight, plant dry weight, total leaf area, dry matter, No of fruits per plant, fruit weight, weight of fruits per plant and total yield, in all pepper genotypes. The genotypes Dandra, Al-Ashraf, Qeft 2, and Esna 2 are stable across the three planting dates, and they are considered relatively heat- tolerant and can be grown on the three planting dates. The first planting date in February was the best.