Exhibit 22.1 Subsidiaries of the registrant

WHOLLY OWNED SUBSIDIARIES

Cleveland, Ohio U.S.A.: Keithley Instruments International Corporation

CHINA: Keithley (Beijing) Measurement Instrument Co.

FRANCE: Keithley Instruments SARL

GERMANY: Keithley Instruments GmbH

GREAT BRITAIN: Keithley Instruments Ltd.

ITALY: Keithley Instruments SRL

JAPAN: Keithley Instruments KK

MALAYSIA: Keithley Instruments Sdn Bhd

NETHERLANDS: Keithley Instruments BV

SWITZERLAND: Keithley Instruments S.A.