This study investigates the global instability caused by shock-wave/boundary-layer interaction of the oblique shock incidence with a Mach number of 2.15 and a Reynolds number of \(1\times 10^5\) using global stability analysis. The results of global stability analysis demonstrate that the boundary layer flow exhibits stationary global instability when the incident angle exceeds \(31.8^{\circ}\) . As the angle further increases, an oscillatory instability mode emerges and becomes dominant as the wavelength decreases. This oscillatory mode evolves into two stationary modes with smaller wavelengths. To determine the global stability effectively, a global instability criterion for interaction between an oblique shock and a laminar boundary layer is established based on triple deck theory. This criterion considers only the the freestream conditions and the shock angles. The overall boundary of the critical scaled ramp angle is in the range of (3.5, 5.5) with respect to the wall-to-freestream temperature ratio ranging from 0 to 12.