A total of 17 Damascus bucks were exposed to different THI conditions during the experimental intervals covering THI of 14.06-21.29 in December (no HS), 22.28-25.14 in March (moderate HS), and 27.19-35.41 in July (severe-extreme HS). Temperature of hair, skin, rectum, and scrotum as well as pulse rate increased (P<0.05) under moderate HS compared to no HS, but further increase (P<0.05) was found in all under severe-extreme HS. Respiratory rate was higher (P<0.05) under severe-extreme HS than under absence or moderate HS. Increasing THI (severe-extreme HS) decreased (P<0.05) RBCs, WBCs, Hb, and Ht to the minimum values, compared to no HS. Plasma concentration of triglycerides, total cholesterol, and very LDL-cholesterol decreased (P<0.05) only under severe-extreme HS. Plasma T3 and T4 concentrations decreased (P<0.05) under severe-extreme HS compared to no or moderate HS. Reaction time was longer and plasma testosterone concentration was lower (P<0.05) under severe-extreme HS than no or moderate HS. Ejaculate volume, and percentages of sperm progressive motility, livability, normality, acrosome integrity, and sperm cell concentration were higher (P<0.05) under no or moderate HS than severe-extreme HS. Sperm output per ejaculate, as total, motile, live, and normal were higher (P<0.05) under no and moderate HS than severe-extreme HS. Body core and surface temperatures, hematology, lipid profile, thyroid function, and semen quality can be reliable monitoring tools for predicting heat stress in goat bucks.