Complex sentence: He received his Ph.D. from the University of Pennsylvania in 1995 under the supervision of Val Tannen, then was a principal member of the technical staff at AT&T Labs until he joined the University of Washington in 2000.
Split into simpler sentences: He received his Ph.D. from the University of Pennsylvania in 1995 under the supervision of Val Tannen. After graduation, he was a principal member of the technical staff at AT&T Labs until he joined the University of Washington in 2000.