X0303 4 2011-03-04 0 0000840883 BTU INTERNATIONAL INC BTUI 0001044321 MARXE AUSTIN W & GREENHOUSE DAVID M C/O SPECIAL SITUATIONS FUNDS 527 MADISON AVENUE, SUITE 2600 NEW YORK NY 10022 0 0 1 0 Common Stock 2011-03-04 4 S 0 2100 12.1686 D 1192967 I By Limited Partnerships Common Stock 2011-03-07 4 S 0 9780 12.1068 D 1183187 I By Limited Partnerships This is a weighted average price. This is a joint filing by Austin W. Marxe (Marxe) and David M. Greenhouse (Greenhouse). They share voting and investment control over all securities owned by Special Situations Fund III QP, L.P. (QP), respectively. 1,183,187 shares of Common Stock are held by QP. The interest of Marxe and Greenhouse in the shares of Common Stock owned by QP is limited to the extent of his pecuniary interest. Austin W. Marxe 2011-03-08 David M. Greenhouse 2011-03-08