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A Theoretical solution for the frequency variation of the four small-signal parameters of a junction transistor has been obtained by extending Shockley's analysis and by taking account of space-charge-layer widening as suggested by J. M. Early. From the results of this solution, it has been possible to explain the experimentally observed frequency variation of open-circuit collector-base admittance of fused-junction p-n-p junction transistors that was reported earlier and is described here in more detail. The theoretical frequency variation of the current-amplification factor and of the other two small-signal parameters (open-circuit voltage-feedback factor h12 and short-circuit input impedance h11, for the grounded-base connection) also is discussed in some detail. Numerical results are included for each of the four parameters in the form of curves of normalized parameters versus relative frequency. Derivation of the voltage-current relations for the theoretical model is given separately in section II. The effect of base-spreading resistance is taken into account in the usual manner by addition of a lumped resistance to the base contact of the theoretical model.