The present disclosure relates to a semiconductor device and a preparation method thereof. The method for preparing a semiconductor device comprises: providing a first dielectric layer; forming a first window in the first dielectric layer; forming a first connection structure in the first window; forming a second dielectric layer on the first dielectric layer, the second dielectric layer having a second window from which at least the first connection structure is exposed; forming a first barrier layer on the sidewall and bottom of the second window, the first barrier layer comprising an opening from which part of the first connection structure is exposed; and forming a second connection structure in the second window.