Instead of passing two parameters to function you can pass the array of two values like this :
$results['args1'] = "value1";
$results['args2'] = "value2";
echo json_encode($results);
and then get it in success function like this :
success:function(results){
jQuery(".semester_selection1").append(results.args1); // This appends value1
jQuery(".semester_selection2").append(results.args2); // This appends value2
}