A new equation was developed for evaluating kinetic parameters in the isokinetic range of a phase transformation using nonisothermal calorimetric techniques. The Johnson–Mehl–Avrami equation was extended by considering that the transformation rate in an isothermal process can be translated into the nonisothermal transformation in an isokinetic range. The Avrami exponent, n, activation energy, E, and frequency factor, K0, were calculated from only one nonisothermal experiment by using the new kinetic equation for amorphous Se (a-Se), polysilane/polycarbosilane (PS/PCS), and lithium disilicate (LiO2 · 2SiO2 or LS2) samples with nucleation site saturation. The values of E and K0 calculated using the new kinetic equation agree well with those obtained by the Kissinger equation for the prenucleated a-Se, PS/PCS, and LS2 samples. The values of n indicate that volume crystallization is dominant in the bulk a-Se and LS2 samples, whereas surface crystallization is dominant in the powdered PS/PCS sample. These results for a-Se were confirmed by scanning and transmission electronic microscopy.