Lentil is one of the most promising legume crops providing nutritional and food assurance to human beings. Due to extensive production of lentil crop in rain-fed agriculture system, its growth and yield are mainly determined by the levels of precipitation. Consequently, it usually faces drought stress during the generative stage resulting in low yield. In such scenario, controlled supplemental irrigation (SI) can improve and stabilize the productivity. Therefore, the present study was conducted to determine the effect of supplemental irrigation on the growth and yield of lentil crop under semi-arid climate conditions of Turkey. An experiment was performed during two consecutive crop seasons at Sanliurfa, Turkey with annual mean rainfall of 196 and 275 mm in the first and second experimental year, respectively. Six supplementary irrigation treatments were given using drip irrigation system [ no supplement irrigation (I-0), 25% (I-25), 50% (I-50), 75% (I-75), 100% (I-100, full irrigation) and 125% (I-125) supplement irrigation depending on the available soil water content]. Results obtained in the study indicated that in both study years, highest biomass, harvest index and grain yield values were obtained from fully irrigated treatments (I-100), while non-supplementary irrigated treatments have provided lowest values. It should be clearly noticed that growth parameters including yield were lower under over-irrigation treatment (I-125). Hence, it is recommended that farmers need to optimize the supplemental irrigation technique to obtain desired yields. This study will support the successful usage of the supplemental irrigation technology to improve lentil productivity, particularly under semi-arid environment.