By considering a simple endogenous growth model, we propose a new theoretical channel through which the presence of asset bubbles can promote economic growth. In the model economy, long-lived value-maximizing firms continuously improve the quality of their specific products through in-house research and development (R&D), while simultaneously new firms enter into the market. The key feature is endogenous market structure: The number of firms is endogenously determined, which leads to variation in firm size measured in terms of the scale of production at the level of an individual firm. The presence of asset bubbles unambiguously gives rise to larger firms. This allows in-house R&D expenditure to be spread over the greater numbers of goods that the firms produce, which can increase incentives to undertake in-house R&D.