Penaeus semisulcatus De Haan, 1844 was collected in Iskenderun Bay, from November 2009 to October 2010, by monthly bottom trawl operations. The male : female ratio was determined as 1: 1, and the spawning period was found to be from January to June, while peaking two times a year, namely in January and in March. The L-infinity and K for males were estimated at 42.00 mm CL and 1.8 year(-1), respectively, and for the females 63.00 mm CL and 1.90 a year(-1). Using the L-infinity and K estimates for both sexes, the instantaneous rate of natural mortality (M) for males and females were calculated as 1.50 and 1.97 year(-1), respectively, at 22 degrees C water temperature on average. The instantaneous rates of total mortalities (Z) were 4.04 year(-1) for males and 6.39 year(-1) for females, and fishing mortalities (F) for males were 2.24 year(-1) and for females 4.42 year(-1). Thus, the exploitation rates (E) were 0.65 year(-1) and 0.69 year(-1) for males and females, respectively. The results clearly indicate overfishing for P. semisulcatus in the study area.