Amorphous microwire in a glass shell has low thermal inertia and can be rapidly heated to the crystallization temperature. We observed the transition process of the microwire from amorphous to microcrystalline state during its heating by pulse current of different amplitudes and durations. The crystallization of amorphous state proceeded in two ways depending on a pulse parameters: “slow” and explosive. In the second case electromagnetic waves emission (light flash) and burst of resistance were observed. The propagation velocity of the crystallization front in our experiments was 1 m/s.