web page postback, how to keep the global variable status

i declare a bool as global variable, by default page is load is false, after the button_On-click function is click, the global variable changing to true. But i cant the the true bool value. Because the code is perform top to bottom. when page is load again the bool value will set to false. Any syntax to perform this ? 
bool check; private void abc_OnClick(object sender, EventArgs e) { check = true; }