The incubation time for the crystallization of amorphous Ge (a‐Ge) films was studied as a function of temperature between 150 and 500 °C by means of bothinsitutransmission electron microscopy and Raman scattering spectroscopy. The temperature dependence of the incubation time for free‐sustaineda‐Ge films follows an Arrhenius curve with an overall (nucleation+growth) crystallization process activation energy of 2.0 eV. In the case where thea‐Ge films were on Si3N4substrates, an earlier stage of the crystallization was observed (nucleation), having an activation energy of 1.3 eV. In addition, it was found that a thin metallic layer of Al or Au, deposited on thea‐Ge films, induces a very fast crystallization in the mode of dendritic growth, as reflected by a low activation energy (0.9 eV) for the incubation time temperature dependence.