The performance of OTFT depends on the gate insulator(GI) and active layer. Therefore, this paper presents C-V characteristics of various gate insulators which may be used in the fabrication of OTFT devices using P3HT as an active layer in order to find the best gate insulator for OTFT devices with P3HT. Poly(4-vinylphenol) (PVP) , poly (vinyl alcohol) (PVA), poly(9-vinylcarbazole) (PVK), benzocyclobutene(BCB) and polyimide(PI) were used as polymer GIs for the soluble process, and poly ( 3-hexylthiophene) ( P3HT) of p-type, which has a relatively high mobility of 0.1 cm2V-1s-1, was selected as an active layer. The C-V of metal-insulator-semiconductor(MIS) was measured and an-alyzed for the drive ability. The spin coating rpm and following bake temperature of P3HT active layer were varied in order to evaluate their effect to the C-V results. The C-V measurement of the fabricated MIS structures were performed at 100 kHz at the bias from to -5 V to 5 V with aO. 1 V step. Also, the C-V measurement frequency was varied to 100 Hz, 1 kHz, 10 kHz and 100 kHz to investigate the low-f and high-f results. The measured capacitances per unit area for of PVP, PVA, PVK, BCB and PI were 1.06, 2.73, 2.94, 3.43 and 2.78 nF/cm2, and threshold voltages were -0.4, -0.7, -1.6,-0.1 and -0.2V, respectively. As the frequency increased, the all capacitances decreased, however the range of the change was only within 1.0-1.5 nF/cm2. The C-V characteristics of the MIS structures were not affected by, and the P3HT thickness or baking condition. It is also suspected that the morphology of P3HT was related with difference of the capacitance and the hole mobility, the combination of PVK and P3HT showed the best result for the OTFT device , which showed continuous capacitance of 3.43 nF/cm2 and the lowest V th of -1.6V.