We have experimentally studied statistical fluctuations of p-n junction depth x(j) of the drain region due to the dopant density variation near the p-n junction edge, whose x(j) was measured by the impact ionization rate alpha, using an 8k MOSFET array test structure, and we have investigated their influence on transconductance G(m) characteristics. The impact ionization rate fluctuation deltaalpha/alpha is experimentally found to be proportional to the square root of the gate oxide thickness T-ox and to be about 0 at T-ox(1/2) = 0, and the average alpha is explained by the usual lucky electron model. Therefore, X-j variation deltax(j)/x(j) can be obtained by this deltaalpha/alpha, because deltaalpha/alpha is caused by the fluctuation of the pinch-off length due to the x(j) variations. Moreover, it was also found that G(m) fluctuation at the saturation region correlates well to the x(j) variations. (C) 2003 Elsevier Science Ltd. All rights reserved.