Organic devices have been attracted for its light weight, flexibility, low cost fabrication. To improve their performance, understanding for carrier injection, accumulation and transport process is needed. However, it is difficult to comprehend these processes by only using indirect methods, e.g., I-V measurement, because of ambiguity of carrier behaviors in organic materials. On the basis of back grounds, we believe that optical methods like second harmonic generation (SHG) method is useful to understand carrier behaviors in organic materials because it can directly probe carrier motion. Using C-V measurements, we have revealed that electron were trapped by photoillumination and biasing in MIS (ITO/PI/P3HT/Au), though the location of electron traps was unknown. In this study, we conducted electric field induced second harmonic generation (EFISHG) and probed the electric field formed by electron traps. We showed the presence of electron traps in PI layers.