The main driving force for High Operating Temperature (HOT) detectors is the strong need for low cost, compact IR imaging solution capable of supporting a wide range of military and civilian applications. In the HOT regime where imagers can be cooled with multi-stage thermoelectric coolers, the major portion of the cost is due to the die-level back-end process, from the chip hybridization to final packaging. We present here an approach to achieve significant cost reduction of MWIR imagers by monolithically integrating III-V devices directly on Silicon substrates for wafer-scale fabrication and packaging of focal plane arrays (FPAs). High quality InAs films can be grown on a blanket Silicon wafer by metal-organic chemical vapor deposition (MOCVD) in a low growth temperature regime that complies with the thermal budget of the Si-electronics. High Resolution Transmission Electron Microscopy reveals predominantly oriented, single-crystal-like InAs films, with Σ3(111) twin boundaries, which our band structure calculations predict to be electrically benign. More intriguingly, selective-area growth on SiO2-masked ROIC-like templates is demonstrated with single-crystal-like InAs film nucleation at small Si(001) openings, together with the suppression of unwanted deposition on the dielectric mask. High crystallinity lateral epitaxial overgrowth of the InAs islands and film coalescence is achieved, enabling the potential to fully cover the entire patterned substrate. MBE-grown MWIR devices (λcut-off = 4.1 μm) on blanket InAs/Si templates exhibit a dark current of 2x10-5 A/cm2 , a specific detectivity of 6x1011 Jones and a quantum efficiency (QE) above 60% at 100K. The QE remains constant at high temperatures (<200K) where the dark current approaches that of baseline single-crystal HOT devices grown on native substrates At 230K, it is 6x10-2 A/cm2, yielding a specific detectivity of 1010 Jones.