Field-enhanced Stokes shifts (FES), i.e. a large downward shift of luminescence peak energy under transverse electric field in excess of quantum confined Stark shift, were observed in strained Si1-yCy/Si quantum wells. The microscopic mechanism of FES is attributed to a carrier heating due to carrier-carrier scattering under transverse:electric field, which allows carriers to relax down to lower energy sites by jumping over kinetic barriers in lateral directions in an inhomogeneous potential of fluctuated heterointerfaces.