The Bombay Stock Exchange benchmark Sensex on Thursday rose by 203 points in opening trade on fresh buying by funds.Sensex was trading at 16440, up by 150 points when reports last came in. Similarly, the wide-based National Stock Exchange index Nifty rose by 47 points to 4,901 points.Brokers said firming trend on the Asian markets following overnight rally in the US markets mainly triggered buying by foreign funds.