A method for making a microfine semiconductor device includes the step of forming a diffusion layer of a small depth to provide reduced junction leak current. Si ions are implanted at a dosage of from 1.times.10.sup.15 to 1.times.10.sup.16 cm.sup.-2 into an Si substrate held at a temperature not higher than -40.degree. C. Then, impurity ion implantation into the Si substrate is conducted so as to form an impurity layer having a depth smaller than that of the amorphous layer. Consequently, it is possible to form an amorphous layer wherein elongation and an increase of dislocation loops at the interface between the amorphous layer and crystalline layer is suppressed. It is also possible to activate the impurity layer through annealing and still provide an impurity layer having a depth smaller than that of the amorphous layer.