A solid‐state alpha dosimeter has been designed and tested suitable for personal and environmental radon/thoron monitoring. The dosimeter basically consists of an electrostatic collector and an alpha‐particle counting system with spectroscopy capabilities. The sensitive volume (∼20 cm3) of the electrostatic collector consists of a cylindrically shaped metal wire screen and a diffused‐junction silicon alpha‐detector covered with a thin aluminized Mylar sheet. A dc voltage (∼500 V) is applied between the wire screen and the Mylar sheet, with the latter held at negative potential relative to the former. Data can be retrieved during or after sampling by means of a microcomputer (Epson HX20) via a RS–232 communication interface unit. The dosimeter has been calibrated in a large (26 m3) radon/thoron test facility. A linear relationship was found between the dosimeter’s alpha‐count and both radon gas concentration and radon daughter working level. The dosimeter is mounted on top of an ordinary miner’s cap lamp battery and is ideally suited for personal monitoring in underground uranium mines and other working areas. The dosimeter presented here is a considerably improved version of an earlier prototype.