At its peak, 9.8 million people - an impressive 47% of the total TV audience - tuned in to see the Time Lord defeat the Daleks, according to BBC figures.
The average viewing figure of 9.4 million is 300,000 more than watched the first episode of the series in April.
The figures for Doctor Who followed days of intense speculation over Tennant's future in the Tardis.
Last week's episode had ended on a cliff-hanger when the Doctor was shot by a Dalek and apparently started to regenerate.
But with the help of a small army of his companions, the Doctor once again thwarted the Daleks and their evil creator Davros to save the universe.
A BBC spokesman said: "We're absolutely delighted with last night's figures and viewers can now look forward to the Christmas Special."
However, Tennant's longer term future as the Time Lord remains uncertain.
He will star in a Doctor Who Christmas special this year and another three specials next year but is not confirmed for the next series in 2010.
The fifth series has been postponed so that the Casanova star can take to the stage to play Hamlet with the Royal Shakespeare Company.