It is shown in this paper that the electromagnetic field yielding a semi-plane-symnmetric metric can be either plane-symmetric or semi-plane-symmetric. If it is plane-symmetric, then it must be a non-null electromagnetic field, while if it is semi-plane-symmetric, then it can be either null or non-null. The general solution of semi-plane-symmetric spacetimes yielded by semi-plane-symmetric sourceless null electromagnetic field is also given in this paper.