Microsoft has bought Semantic Machines, an artificial intelligence start-up, as it looks to boost its efforts in developing conversational AI.

Berkeley, California-based Semantic's approach to AI is using machine learning to add context to conversations with chatbots. This means taking information received by AI and applying it to future dialogue.

The firm's speech recognition team previously led automatic speech recognition development for Apple's personal assistant Siri.

In its announcement Monday, Microsoft did not disclose any financial details of the acquisition.

Big players are trying to make their personal assistants more human-like. Amazon has said it is aiming to give Alexa a "memory" and add more context to conversations, while Google demonstrated a chat between a hairdresser and a human-like version of its assistant that booked an appointment on behalf of someone else.

"With the acquisition of Semantic Machines, we will establish a conversational AI center of excellence in Berkeley to push forward the boundaries of what is possible in language interfaces," David Ku, chief technology officer at Microsoft AI and Research, said in a blog post.

"Combining Semantic Machines' technology with Microsoft's own AI advances, we aim to deliver powerful, natural and more productive user experiences that will take conversational computing to a new level."

AI-powered personal assistants are core to voice-activated speakers like Amazon's Echo and Google's Home. Microsoft hasn't built its own smart speaker but partnered with audio firm Harman Kardon in 2016 to integrate its Cortana assistant with a smart speaker called Invoke.