After six months, you are expected to return to your home country and not overstay your visa (so you must return while you still have a valid visa). However, you can request a visa extension, provided you prove you need more time to complete your business affair in the United States. To apply to the US Citizenship and Immigration Services (USCIS) and request to extend visa validity, you must acquire letters of confirmation from your employer or company that prove your stay in the US is essential for business.