The recorded minutes of Senate hearings are not made available to the public as of 2015. However, congressional committee hearings are available. These committee hearing transcripts can take up to a few years before they are published, according to the United States Senate website.
The prepared witness testimony is usually available much earlier. This online testimony lacks the question-and-answer part of the hearing. Most of the hearings are organized online by the date. Many college libraries and some of the bigger library systems also offer access to hearings through the Federal Depository Library Program. Hearings that have been published can also be purchased from the government through the Government Printing Office.