Response of PIN diode is numerically simulated by a self-developed 2D semicon- ductor device simulation GSRES to study the response behavior of PIN diode limiter under electromagnetic pulse (EMP). Current overshoot phenomena of PIN diode during the rise time of EMP, which is validated to be due to the capacitive performance of PIN diode under high frequency, are analyzed. Shorter rise time of EMP causes higher current peak value. Overshoot current is affected by the impurity doping concentration of PIN diode. Higher doping concentra- tion of impurity in the P layer and N layer causes higher peak of current and sooner attenuation of overshoot current. Doping concentration of the I layer affects the overshoot current too, but not as salient as concentration of the P and N layers. These results can be used in radiation hardening for PIN diode limiter. Electronic systems are used more and more widely in industryeconomic and science research as key equipment. Semiconductor devices, as basic component, determines the performance of electronic system. Since the development of manufacturer techniques, operation power of device becomes much lower than before, and therefore, much more susceptive by electromagnetic pulse (EMP). For these reasons, study of the effects of semiconductor devices in electronic system under EMP is now becoming immediately demand not only for industrial application but also in infor- mationize process. PIN diode, which is used as a component in communication and radar systems, is also the key component of PIN limiter, so the study of its effect under EMP is important in electronic equipment harding and shielding. Comparing with experimental method, numerical simulation of semiconductor devices can re- flect the physical phenomena and mechanisms of devices, and is important in effect study. It is proved to be efficient and accurate as many research results showed [1–3]. One-dimension numerical simulation result of PIN diode under step voltage pulses with risetime less than 0.1 ns is obtained [4] and overshoot current phenomenon appears. Characters of PIN diodes in EMP field are researched by equivalent circuit models [5, 6]. Also, abecedarian study of response of PIN diode under EMP is developped [7]. In this paper, relationship between overshoot current of PIN diode under EMP with the risetime of pulse and relationship between overshoot current of PIN diode under EMP with den- sity of impurity of diode are studyed numerically by a simulator GSRES (General Semiconductor Radiation Effect Simulator).