We have developed a new laser ablation type cluster source named 'spatiotemporal confined cluster source' (SCCS), which gives well-defined thermo-dynamical conditions for cluster growth with narrow size dispersion. A laser-induced shock is controlled to produce a definite mixed gas layer of the silicon vapor and helium gas, which is locally confined in a sub millimeter space, and conserved densely for a time of 160 mus. The generated silicon clusters, which are ionized by an ArF excimer laser for mass analysis without dissociation, show narrow size dispersion with characteristically higher abundance of stable Si23Hx (46%), S19Hx (14%), and Si21Hx (12%) clusters. (C) 2002 Published by Elsevier Science B.V.