Methods of forming gate-all-around transistors which include a germanium-containing nanowire and/or an III-V compound semiconductor nanowire. Each method includes the growth of a germanium-containing material or an III-V compound semiconductor material that includes an upper portion and a lower portion within a nano-trench and on an exposed surface of a semiconductor layer. In some instances, the upper portion of the grown semiconductor material is used as the semiconductor nanowire. In other instances, the upper portion is removed and then a semiconductor etch stop layer and a nanowire template semiconductor material of a Ge-containing material or an III-V compound semiconductor material can be formed atop the lower portion. Upon subsequent processing, each nanowire template semiconductor material provides a semiconductor nanowire.