SAN FRANCISCO — A Los Altos expert witness has sued King & Spalding, saying partners at the firm let invoices for work done on a huge International Trade Commission case go unpaid while blaming a bankrupt former client for the lapse.

Michael Thomas, who specializes in semiconductor technology, accuses the firm of bilking him out of $34,000. In 2008 King & Spalding and a handful of other law firms retained Thomas to provide expert witness consulting for an ITC hearing. In that matter, a Milpitas-based semiconductor manufacturing company accused 18 companies, including King & Spalding client Qimonda AG, of patent violations.