The pattern for as soon as. . . is made by attaching the one-shape ending -자 to verb bases. The pattern is usually intensified in spoken language with 마자: 오자 or 오자마자 as soon as [someone] comes/came. Note that even if the event in the second clause is past, the verb with the -자마자 ending still attaches to a plain base – the verb at the end of the whole sentence does all the work of showing the tense. Here are some more examples:
- 내가 서울역에 도착하자마자, 기차가 떠났어요.
The train left as soon as I arrived at Seoul station. - 수업이 끝나자마자 점심을 먹으러 갈 겁니다.
We’re going to go eat lunch as soon as class finishes. - 숙제를 마치자마자, 집에 돌아갔어요.
He went home as soon as he finished his homework. - 밥을 먹자마자 손님이 왔어요.
I had no sooner eaten than someone came. - 부산에서 내리자마자 사촌 동생을 만났어요.
I saw (or met) my cousin as soon as I got off at Pusan. - 방학이 되면 시골에 쉬러 가고 싶습니다.
As soon as vacation comes, I want to go to the countryside to take a rest. - 버스에서 내리자마자 비가 쏟아졌어요.
As soon as I got off the bus, it poured.