What is the penalty for thoughtcrime?

In general, the penalty for thought crime is death.  That is, after all, what happens to Winston.

We also know that this is the case because Winston knows that he is dead as soon as he starts writing in the diary.

However, the penalty is not just death.  When they catch Winston, they don't just bring him off somewhere and shoot him.  Instead, they torture him first.  They do this so that they can get him to actually stop believing in his "criminal" thoughts.  It is only after that that they kill him.