Ex University of Bedfordshire academic Dr Theodora Dallas told jurors a man on assault charges at Luton Crown Court had previously been accused of rape.
The trial in July 2011 was halted. Dallas, from Greece, said her grasp of English was sometimes "not that good".
Three High Court judges sentenced the 34-year-old to six months in prison.
She was told that she would serve three months in jail and be on licence for the remainder of the term.
The judges refused Dallas permission to appeal to the Supreme Court.
Lord Judge said Dallas had "deliberately disobeyed" the trial judge's instructions not to search the internet and added: "The damage to the administration of justice is obvious."
He said: "Misuse of the internet by a juror is always a most serious irregularity and an effective custodial sentence is virtually inevitable."
Her counsel Charles Parry had made a plea to the court to be merciful and impose a suspended sentence, but Lord Judge rejected this.
He said there was "no sufficient basis" for suspension.
She had said earlier in a written statement: "I had no intention at all to prejudice the jury in any way. I had no intention to disobey what the judge said."
At a hearing last Thursday, Attorney General Dominic Grieve told Lord Judge, Lady Justice Hallett and Mr Justice Openshaw that Dallas had impeded the administration of justice and was in contempt.
But the academic, who has resigned from her post, told the judges: "I did not understand that I could make no search on the internet.
"I really apologise. I never thought it would cause such disruption."
Lord Judge said Dallas was guilty of "contempt of the jury and the jury system... to the criminal standard".
"In the long run, any system which allows itself to be treated with contempt faces extinction.
"That is a possibility we cannot countenance."
Dallas came to England from Greece at the age of 19 and was "a woman of positive good character and we acknowledge her achievements thus far in her relatively young life," the judge said.
"She has now put her academic career into jeopardy."
But nothing had been said in mitigation that convinced the court she should be spared an immediate jail sentence, the judge said.
He had "no doubt" that Dallas knew "perfectly well" the trial judge had directed members of the jury not to seek information from the internet but "deliberately disobeyed the order".
"She did not merely risk prejudice to the due administration of justice, but she caused prejudice to it.
"The time of the other members of the jury was wasted and the public was put to additional unnecessary expense."
Dallas had been a psychology lecturer at the University of Bedfordshire, which has its main campus in Luton.
The trial where the contempt was committed involved a man accused of causing grievous bodily harm with intent.
A juror had told an usher that Dallas had carried out internet research while they were deliberating their verdict, flouting instructions by the trial judge.
Dallas had revealed to jurors the man had previously been accused and acquitted of rape. He was re-tried in October last year, convicted and jailed.
Dallas said she had been checking the meaning of grievous bodily harm on the web.
She had added the word "Luton" to a search which produced a newspaper report mentioning the man and the rape allegation.
A juror who researched a defendant's past on the internet and shared the information with fellow jury members has been jailed for contempt of court.