  Radio-frequency dispersive read-out can provide a useful probe to nano-scale
structures such as nano-wire devices, especially when the implementation of
charge sensing is not straightforward. Here we demonstrate dispersive
`gate-only' read-out of phosphor donors in a silicon nano-scale transistor. The
technique enables access to states that are only tunnel-coupled to one contact,
which is not easily achievable by other methods. This allows us to locate
individual randomly placed donors in the device channel. Furthermore, the setup
is naturally compatible with high bandwidth access to the probed donor states
and may aid the implementation of a qubit based on coupled donors.
