at the top of：

1.I waited at the top of the stairs. 我在楼梯顶端等着。

2.He stopped at the top of the stairs. 他在楼梯顶端停了下来。

3.They paused at the top of the stairs, doubtful as to which way to go next 他们在楼梯顶部停住了，不知道接下来该往哪边走。