In this work, we report a novel Indium Arsenide-on-insulator (InAsOI) FinFET platform designed with record high aspect ratio that favors the use of the devices as charge sensors. InAs has very high mobility among III-V semiconductors and an intrinsic surface accumulation layer yielding good ohmic contacts thus making it an interesting choice for chemical and biological sensing platforms. Template Assisted Selective Epitaxy (TASE) enables the integration of III-V highly scaled devices, monolithically integrated on Silicon, within a fully CMOS compatible fabrication scheme hence without any catalyst-induced growth. With a new geometry, high-aspect-ratio (HAR) InAs fins and a new application of pH sensing the versatility of TASE is exhibited. HAR InAs fins, fin height to fin width in excess of 4 for fin width down to 30 nm are fabricated on a Si substrate. The HAR InAs-on-insulator fins are characterized as pH sensors. A sensitivity of 38.8 mV per pH is extracted at 6μA drain current from a 40 nm wide 20 multi-finger array.