A semiconductor device includes an inorganic insulating layer on a semiconductor substrate, a contact plug that extends through the inorganic insulating layer to contact the semiconductor substrate and a stress buffer spacer disposed between the node contact plug and the inorganic insulating layer. The device further includes a thin-film transistor (TFT) disposed on the inorganic insulating layer and having a source/drain region extending along the inorganic insulating layer to contact the contact plug. The device may further include an etch stop layer interposed between the inorganic insulating layer and the semiconductor substrate.