This paper is one of a series providing a comprehensive study of cyclotron resonance and impurity transitions for n-type GaAs, InP, CdTe and CdSe. In this paper, attention is concentrated on weak transitions which can be observed when the electrons are predominantly bound to the donor states if the photon energy is insufficient to excite the electrons from the ground state of the donor. With all materials the most prominent lines observed are found to lie on the same curves of excitation energy against magnetic field. The following transitions are positively identified 2p-+ 2s; 2p- ,-f 3s; 2p-, + 3d-I ; 2p-f 3d,. 2p0 + 3s, 2p0 + 3d+,.2s-f 3p+,,and3d-, + 3p-,.Thedependenceoftheselinesontemperature and impurity content is discussed and compared with the cyclotron resonance lines.