The two-dimensional (2D) electron and hole energy relaxation associated with acoustic phonon emission in n- and p-type modulation doped Ga0.7In0.3NyAs1–y/GaAs quantum wells has been investigated experimentally using Shubnikov-de Haas (SdH) effect measurements performed as a function of lattice temperature and applied electric field. Nitrogen concentration dependence of the effective mass and quantum lifetime of the 2D electrons in the n-type samples have been determined from the temperature and magnetic field dependencies of the amplitude of SdH oscillations, respectively. The in-plane effective mass of the 2D electrons increases when the nitrogen mole fraction is increased from y = 0.004 to 0.010 but remains the same when it is increased to y = 0.015. The values obtained for quantum lifetime suggest that interface roughness is the dominating scattering mechanism in n-type Ga0.7In0.3NyAs1–y/GaAs quantum wells. The electron temperature (Te) of hot electrons and the hole temperature (Th) of hot holes have been obtained from the lattice temperature (TL) and applied electric field dependencies of amplitude of SdH oscillations. The experimental results for the electron/hole temperature dependence of power loss are compared with the current theoretical models for power loss in 2D semiconductors, which include both piezoelectric and deformation-potential scattering. For n-type samples, the power loss from the electrons is found to be proportional to (T–T) with γ in the range from 3.48 to 4.66, indicating that the energy relaxation of electrons is due to acoustic phonon emission via unscreened piezoelectric interaction. For the p-type sample, the power loss is approximately proportional to (T–T). This behavior is in accord with the theoretical predictions for the variation of power loss with hole temperature for a 2D hole gas in the equipartition regime.