Abstract: A method includes epitaxially growing a Ge1-xSnx channel layer over a substrate. The Ge1-xSnx channel layer is in a metastable state. A Ge1-ySny barrier layer is epitaxially grown over the Ge1-xSnx channel layer to form a two-dimensional hole gas in the Ge1-xSnx channel layer. The Ge1-xSnx channel layer and the Ge1-ySny barrier layer are etched to form a first opening and a second opening in the Ge1-xSnx channel layer and the Ge1-ySny barrier layer. A first source/drain electrode and a second source/drain electrode are deposited in the first opening and the second opening, respectively. A gate electrode is formed over the Ge1-ySny barrier layer.