Electrical characteristics of the mechanically flexible driver LSI as thin as 35 µm mounted directly on a flexible display panel were precisely analyzed. The high-voltage transistors on this LSI show the current decrease by 10-30% in high voltage region, comparing with that of an ordinary thickness LSI. These phenomena can be associated with a self-heating effect. We considered the thermal diffusion on the thin chip by changing material of the measurement stage. Moreover, we analyzed the transistor characteristics on the thin chip under convex and concave bending conditions. The drain current change by piezoresistive effect was observed.