The comparative analysis of solar flares by GOES class M obtained with the Bauman Moscow State Technical University radio telescope RT-7.5 at frequencies of 93 and 140 GHz is presented. A positive slope of the sub-THz flux density spectrum was revealed for three flares between frequencies 93 and 140 GHz. The observational characteristics of these flares involving data in the X-ray, ultraviolet, and microwave ranges were described.