The quaternary barrier InAlGaN is suitable for GaN HEMT power microwave applications. High doping of semiconductor under the drain and source is a known suitable solution to achieve low ohmic contact resistance. However, InAlGaN quaternary alloys require low thermal budget to avoid indium desorption from the active layer during regrowth and thus deteriorating the barrier. This article presents a selective area growth technique at 850 °C by MOVPE to achieve low contact resistance with respect of temperature constraint. Regrowth temperature and mask geometry were investigated to achieve selectivity and control of the regrowth rate. The use of H2 as carrier gas decomposes the GaN buffer layer and damages the surface creating material cluster during regrowth. Growth with N2 carrier gas shows non-selective epitaxy, as there are deposits on the entire surface of the dielectric mask. Switching from one carrier gas to another depending on the step in the MOVPE reactor helps to control both the morphology and selectivity. The resulting high doping levels of 8 × 1019 cm-3 leads to a low contact resistance of 0.26 Ω.mm.