A recessed portion in a semiconductor substrate and a method of forming the same are provided. The method comprises: forming a mask on the semiconductor substrate; forming a protection layer on a top surface of the mask and on at least one sidewall of the mask, and on at least one surface of the semiconductor substrate exposed by the mask; performing a first etching process to remove the protection layer on the top surface of the mask and on a bottom surface of the semiconductor substrate exposed by the mask; and performing a second etching process to remove the remaining protection layer and to etch the semiconductor substrate to form the recessed portion. In this way, a recessed portion with relatively smooth and vertical sidewalls can be realized.