Thin film transistors(TFT) were made based on the polycrystalline Si (poly-Si) crystallized by sequential lateral solidification(SLS) method. The electrical characteristics of the devices were analyzed. n-type TFTs did not show a superior characteristics compared to p-type TFTs. We analyzed the causes of the failure by focused ion beam(FIB) analysis and automatic spreading resistance(ASR) measurement, to study the structural integrity and the doping distribution, respectively. FIB showed no structural problems but it revealed a non-intermixed layer in the contact holes between the polysilicon and the aluminum electrode. ASR analyses on poly-Si layer with various doping concentrations and activation temperatures showed that the inadequately doped areas were partially responsible for the inferior behavior of the whole device.