" Ask the US people to contact directly the Korean prof for his reco for you." THIS IS NOT A GOOD SUGGESTION Have some courage. Throw the reco letter form to your Korean prof. and ask him to send it US himself. Tell him whatever he writes about you is acceptable to you with respect. Then you send your all application documents to US and so US will also ask reco at least by Email from Korean Prof. THIS IS NOT GOOD EITHER. My 2 paisa ko suggestion - just email the US profs and let them know that you cannot get your advisor's reco and give them the reason/s behind it. If you'll let your advisor know about your plans of ditching him he may not take it kindly. What would happen in case you get rejected by all the US universities u've applied to and you have no other option than continue working with your current advisor?