We investigate the effect of the parasitic access resistance on device parameters, particularly the threshold voltage (VT) and the contact resistance (RC), of staggered organic field-effect transistors by varying the active layer thickness (ds). At low gate voltages, RC decreases as ds increases due to the free carrier density increasing in the semiconductor film. At high gate voltages, RC increases as ds increases due to increasing access resistance. These factors degrade the device parameters with increasing ds. The contribution of the change in ds on the VT shift is assessed by subtracting the contact effect from the apparent VT.