Defendant must obtain a certificate of probable cause to appeal based on ineffective assistance of counsel regarding request to withdraw guilty plea. Following his guilty plea pursuant to a plea agreement, Johnson subsequently indicated that he wished to change his plea and the trial court conducted a hearing pursuant to People v. Smith (1993) 6 Cal.4th 684 (a post-conviction Marsden hearing) to determine whether substitute counsel should be appointed to investigate grounds for withdrawal of the plea based on ineffective assistance of counsel. The trial court denied Johnson’s motion to set aside the plea and he was sentenced. He filed a notice of appeal and a request for certificate of probable cause. The trial court denied the request for a certificate of probable cause. Appellant subsequently filed an amended notice of appeal which stated that the appeal was based on matters occurring after the plea, not challenging its validity. On appeal, Johnson argued that he was denied the right to effective assistance of counsel because the attorney did not attempt to support the motion to withdraw the plea. The appellate court dismissed the appeal, concluding that a certificate of probable cause was required. The California Supreme Court granted review to resolve a conflict among appellate court decisions addressing the issue of whether a defendant who desires to appeal based on his counsel’s ineffective assistance regarding the defendant’s request to withdraw a guilty plea must first obtain a certificate of probable cause. The Court affirmed the judgment of the appellate court, agreeing with People v. Emery (2006) 410 Cal.App.4th 560 and disapproving People v. Osorio (1987) 194 Cal.App.3d 183. Adoption of the Osorio rule would undermine both the purpose of section 1237.5 of avoiding the cost of frivolous appeals, and the holding in People v. Ribero (1971) 4 Cal.3d 55, that an appeal of a denial of a motion to withdraw a plea requires a certificate of probable cause.