We present a multi channel Schottky-barrier (SB) field effect transistor (FET) based platform for chemical sensor applications and investigate its sensitivity on channel length. Designed transistors consist of parallel assembled bottom up grown silicon nanowires with a mean diameter of 20 nm. Focusing on investigations of devices with different channel lengths, we demonstrate that different optimum sensing regimes exist and they are determined by the device geometry. These target at different realizations and operation schemes. The sensitivities of the SB-FETs in linear and subthreshold regime are extracted from analysis of the pH response of silicon nanowire sensor devices.