2 Kings 15:30

And Hoshea the son of Elah made a conspiracy against Pekah the son of Remaliah, and smote him, and slew him, and reigned in his stead, in the twentieth year of Jotham the son of Uzziah.

Hoshea the son of Elah made a conspiracy against Pekah the son of Remaliah, and smote him, and slew him. It is highly probable that the discontent and disorders consequent upon the sufferings of the people, through so extensive a portion of the kingdom of Israel, originated the conspiracy by which, in the year following, Pekah's throne became vacant.

And reigned in his stead, in the twentieth year of Jotham the son of Uzziah. The murder of Pekah introduced a period of anarchy, which lasted nine years, and was terminated by Hoshea's success in establishing himself on the throne (see further the note at 2 Kings 17:1). Jotham's reign having lasted only sixteen years, the meaning is, that the reign of Hoshea began in the twentieth year after the beginning of Jotham's reign: the sacred historian, having not yet introduced the name of Ahaz, reckoned the date by Jotham, whom he had already mentioned (see the notes at 2 Chronicles 27:8).