The physical processes of charge collection and gas multiplication of a Micro Pixel Chamber (mu-PIC) were studied in detail using a three-dimensional (3D) simulation. The collection efficiencies of primary electrons and gas multiplication factors were calculated for several electrode structures. Based on those studies, we analyzed the optimization of the electrode structure of the mu-PIC, in order to obtain a high gas gain of more than 104 and a simultaneous suppression of discharges. Consequently, we found that these characteristics strongly depend on the substrate thickness and the anode diameter of the mu-PIC. In addition, a gas gain of 105 would be expected for a mu-PIC having a thick substrate of > 150 mu m. (c) 2005 Elsevier B.V. All rights reserved.