答案是否定的。

看具体例句：

His plan is to build a new house. He has given up his plan to build a new house.

前句中不定式作表语（名词性表语，A=B）。后句中不定式通常被分析为定语表示同位关系，而不是分析为同位语。

His job is cleaning the office. He is afraid of losing his job of cleaning the office.

前句中动名词作表语。后句中动名词需要介词过渡，介词短语作后置定语表示同位关系。