Abstract: A first p-type silicon layer (3) is formed as a buried layer in a p-type single crystal silicon substrate (2), and an n-type silicon layer (4) is formed on the upper side of the silicon substrate (2). A second p-type silicon layer (5) for forming an opening is defined in the n-type silicon layer (4), and a metal protecting film (14) is formed on the upper side of the n-type silicon layer (4). An electrode layer (18) is formed on the rear side of the silicon substrate (2) via an oxide film (17). The electrode layer (18) and the silicon substrate (2) are electrically connected to each other via a connecting opening (17a) at portions aligned with the first p-type silicon layer (3). After a positive terminal and a negative terminal of a DC power source (V) are connected to the electrode layer (18) and to a counter electrode (11) respectively, a voltage is applied between the electrode layer (18) and the counter electrode (11) to carry out anodization.