A simple method to measure and analyse the factors affecting the maximum frequency of oscillation of transistors is described. From the maximum frequencies of oscillation measured with certain external series resistances connected in the base and collector circuits, the frequency of zero db current gain fT, base resistance rb, collector capacitance Cc, and also the intrinsic characteristic frequency fTd of the transistor can be deduced. The method of analysis is also discussed in the case when the collector conductance introduced by base width modulation plays an important role in limiting the maximum frequency of oscillation of the transistor. The connection between the maximum frequency of oscillation of drift transistor and its external parameters is discussed finally. It is concluded that when proper corrections are made for drift transistors, not only fTd, rb, and Cc, but also the magnitude of drift field in the base region of drift transistors can be deduced.