We have been developed an electron tracking Compton camera (ETCC) using an SOI pixel semiconductor detector for observation sub MeV gamma rays. An electron tracking Compton camera can reconstruct arrival directions of gamma rays event by event as a point using the recoil directions of electron tracks , so this camera does not increase false spot comparing with a classical Compton camera. Also, an ETCC can discriminate between the gamma rays and backgrounds by detecting the track length and energy of recoil electro…