We have performed thermal measurements and electrothermal simulations (finite element modelling) with the aim of optimizing the power consumption and the temperature distribution of micro-hotplates for gas-sensing applications. A silicon island was added underneath the membrane of the micro-hotplate to improve the temperature distribution of drop-coated metal-oxide gas sensors and to thermally isolate MOSFET gas sensors. The temperature distribution over the sensing area and the power consumption depend on the silicon island thickness, which was optimized for both applications using the software MEMCAD from Microcosm Technologies. In the optimization process, we considered the thermal conductivity of silicon and dielectric membrane, the operating temperature, the geometry and the area of the heater, and the processing of the silicon island. The thickness of the silicon island was optimized to ensure a good temperature distribution over the gas-sensing area for metal-oxide and MOSFET gas sensors with specific geometry.