  The Shafarevich conjecture for K3 surfaces asserts the finiteness of
isomorphism classes of K3 surfaces over a fixed number field admitting good
reduction away from a fixed finite set of finite places. Andr\'{e} proved this
conjecture for polarized K3 surfaces of fixed degree, and recently She proved
it for polarized K3 surfaces of unspecified degree. In this paper, we prove a
certain generalization of their results, which is stated by the unramifiedness
of l-adic \'{e}tale cohomology groups for K3 surfaces over finitely generated
fields of characteristic 0. As a corollary, we get the original Shafarevich
conjecture for K3 surfaces without assuming the extendability of polarization,
which is stronger than the results of Andr\'{e} and She. Moreover, as an
application, we get the finiteness of twists of K3 surfaces via a finite
extension of characteristic 0 fields.
