In 1990 he graduated from the Paris Conservatoire with grants of Premiere Prix in piano and chamber music and the same year won third prize(no first prize was allocated this year) from the Chopin International Piano Competition and also the Sonata prize. With this success, Yokoyama then officially began his concert activities, including recitals and performances with orchestras in cities all around the world, in addition to chamber music and radio broadcast performances. He performed with renowned Orchestras such as Vienna Chamber Orchestra, Berlin Symphony Orchestra, St. Petersburg Philharmonic Orchestra, Budapest Festival Orchestra, Gothenburg Symphony Orchestra, NHK Symphony Orchestra among others. In 1999, his CD recording of Liszt's Etudes of Transcendental Techniques won the twenty-fifth International Liszt Grand Prix for a new recording. This award is unique in that the 10 judges listen to the CDs with the names of all performers covered up, insuring that judgement is based only on the recordings themselves. Some past winners of the award include such renowned pianists as Horowitz, Richter, Pollini among others. He recently began composing mainly piano works on his own.