Federal judges serve "during good behavior." This means that unless a judge commits an impeachable offense, every federal judge serves for life.
Most students learn in junior high school about the balance of power in the United States government and how the executive, legislature and judicial branches provide checks and balances for each other. But how can federal judges stay independent when they are appointed by the president and confirmed by the U.S. Senate? The framers figured it out.
TL;DR (Too Long; Didn't Read)
Federal judges serve "during good behavior." This means that, unless a judge commits an impeachable offense, every federal judge serves for life.
Federal Court System
The federal court one hears about most is the United States Supreme Court. It is the highest court in the land. There is no appeal from a decision of this court. The federal court system also includes 94 district-level trial courts termed district courts, and 13 courts of appeals. District court decisions can be appealed to the court of appeals and court of appeals court decisions can be heard on appeal by the Supreme Court.
During Good Behavior
As the framers struggled to design a government for the United States, the balance of power was a fundamental building block. Congress would make laws, the president and the executive branch would implement them and the judicial branch would interpret them and determine if they lined up with the principals of the Constitution.
To implement this idea, it was essential that judges be independent. Under the Constitution, federal judges are all nominated by the President and confirmed by the United States Senate. If these judges could be readily removed by the President or Congress or have their salaries cut, they would be under pressure to make rulings desired by the other branches. For that reason, the founders built the concept of an independent judiciary into the Constitution.
Article III of the United States Constitution provides that the salaries of federal judges may not be diminished after they are hired. (Currently, federal district court judges make $208,000, circuit court judges $220,600, Supreme Court justices $255,300 and the chief justice $267,000.) Article III also states that judges hold office "during good behavior." This applies both to Supreme Court justices and lower federal court judges as well, such as federal district court judges.
Exactly what does "during good behavior" mean in this context. It means that the judges serve for life, as long as they do not commit serious offenses, or until they voluntarily quit.
Impeachment for Bad Behavior
The Constitution does not define what "good behavior" for federal judges means. It does, however, talk about bad behavior in its discussion of impeachment. And in fact, the impeachment process is the only way federal judges can be removed from office.
The U.S. Constitution discusses the types of offenses a judge can be impeached for. They include treason, bribery and other “high crimes and misdemeanors.” Impeachment charges are brought in the House of Representatives by a vote of the majority of the members. If this happens, the judge is said to be impeached. But for the judge to be removed, the United States Senate must "convict" by a two-thirds vote.
This doesn't happen very often. In the over 200 years that the United States has been a nation, only 15 federal judges have been impeached. Of those, only eight have been convicted and removed from office. Three others resigned from the bench after impeachment to avoid a conviction in the Senate.