In this paper, a micro electromechanical systems vertical-cavity surface-emitting laser (MEMS-VCSEL) with asymmetric double oxide aperture and highly strained GaInNAsSb quantum wells for widely tunable, single mode and high temperature operation has been investigated. The MEMS-VCSEL is based on an integrated two-chip concept which allows us to extend the single wavelength performance to a continuously tunable, selectively wavelength-addressable spectrum of 40 nm. It has a much larger tuning range as compared with previous works. We present a comprehensive model including electrostatic membrane equation coupled with thermal, spatial and temporal rate equations considering Shockley Read Hall (SRH), Auger and carrier diffusion effects. These coupled equations are solved numerically by finite difference method (FDM). Using the simulation results, we design a single mode, high power, high temperature and tunable VCSEL, which is suitable for C-band dense-wavelengthdivision-multiplexing (DWDM) optical communication systems.